Air control device including air switching valve driven by motor

ABSTRACT

An air control device is advantageously used as a device for supplying secondary air to a catalyzer contained in an exhaust pipe of an internal combustion engine. The air control device includes an electric motor, a speed reduction mechanism, a valve having a valve shaft and a biasing spring. These components are all contained in a housing that has a valve port formed therein. The valve is driven to open the valve port by the electric motor against a biasing force of the biasing spring. A rotational movement of a final gear in the speed reduction mechanism is converted into a linear movement of the valve shaft to thereby open the valve port. Since the biasing spring such as a torsion spring is wound around a flange connected to an axis of the final gear, a length of the valve shaft is made short, and the device as a whole is made compact.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority of Japanese Patent Application No. 2005-209613 filed on Jul. 20, 2005, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a valve for switching a fluid flow such as airflow, the valve being driven by a driving mechanism including a driving motor.

2. Description of Related Art

An airflow control valve for controlling an amount of air flowing through an air passage connected to an exhaust pipe of an internal combustion engine has been known. The airflow control valve is driven in an on-off fashion by a driving mechanism including an electric motor and a speed reduction mechanism having plural gears. A final gear in the speed reduction mechanism is engaged with a rack formed on a valve shaft which is reciprocated to open or close a valve port. Examples of this kind of airflow control valve are disclosed in JP-A-6-173783 and JP-A-11-62724.

A coil spring for biasing the valve head toward an open position or a closed position of the airflow control valve is disposed around the valve shaft. Since the coil spring is disposed around the valve shaft, it is unavoidable to make the valve shaft longer by a length of the coil spring to secure a space for the coil spring. Accordingly, the airflow control valve becomes large in size, requiring a large mounting space.

Some of the airflow control valves such as EGR (Exhaust Gas Recirculation) valves are connected in a cantilever fashion to an air passage communicating with a combustion chamber of an internal combustion engine. More particularly, a housing containing a motor, a speed reduction mechanism and a valve therein is connected to the air passage at a position opposite to the motor in a cantilever fashion. If the valve shaft is long in its axial direction, a distance from the mounting portion of the housing to the motor becomes long, and the housing has to be made stronger to endure vibration of the engine. When the speed reduction mechanism is severely vibrated, a relative movement between a rack of the valve shaft and a final gear of the speed reduction mechanism engaging with the rack is generated, and thereby abrasion wear occurs in the rack and the final gear.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved air control device including an air switching valve, which is made compact in size by making the valve shaft short. Another object of the present invention is to improve its mechanical strength against vibration and to suppress the abrasion wear of the rack and the final gear.

The air control device of the present invention is advantageously used as a secondary air control device for an internal combustion engine mounted in an automotive vehicle. The air control device supplies secondary air sent from an air pump to a catalyzer, such as three-way catalyzer, disposed in an exhaust pipe for purifying exhaust gas. The secondary air is supplied to the catalyzer to warm it up to thereby activate it when a temperature of the catalyzer is low.

The air control device includes a housing having a valve port formed therein, an electric motor, a speed reduction mechanism having plural gears for transmitting a rotational torque of the motor at a reduced speed, a valve for opening or closing a valve port, and a biasing spring for biasing the valve in a direction to close the valve port. The valve is composed of a valve head sitting on a valve seat and a valve shaft connected to the valve head. The valve shaft includes a rack engaging with a final gear of the speed reduction mechanism. A rotational movement of the final gear is converted to a linear movement of the valve shaft. The biasing spring is disposed around an axis of the final gear. When the electric motor is energized, the valve shaft of the valve is driven in a direction to open the valve port against the biasing force of the biasing spring, and thereby the valve port is open to supply the secondary air to the catalyzer.

The housing containing components of the air control device therein is connected to an air passage communicating with the valve port in a cantilever fashion. The valve may be biased in a direction to open the valve port so that the valve port is closed when driven by the electric motor. The electric motor may be replaced with other drivers such as an electromagnetic solenoid. The air control device may be used for re-circulating exhaust gas into an engine in a controlled manner. Preferably, the biasing spring is a torsion spring wound around a flange connected to the axis of the final gear.

Since the biasing spring is disposed around the axis of the final gear, instead of disposing it around the valve shaft, a length of the valve shaft can be made shorter. Accordingly, the air control device can be made compact, and its mechanical strength against engine vibration can be improved when the housing is mounted on the air passage in a cantilever fashion. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a structure of a valve-driving mechanism used in an air control device of the present invention;

FIG. 2 is a cross-sectional view showing an entire structure of a secondary air control device for an internal combustion engine;

FIG. 3 is a cross-sectional view showing the valve-driving mechanism; and

FIG. 4 is a plan view showing a speed reduction mechanism of the secondary air control device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described with reference to accompanying drawings. The present invention is applied to a secondary air control device for an internal combustion engine mounted on an automotive vehicle. The secondary air control device is used in a system for supplying secondary air to a three-way catalizer in an exhaust pipe to warm up and quickly activate it when a temperature of the exhaust gas is low at a starting up of the engine, for example. An air pump is connected to the secondary air control device through a secondary air passage.

Referring to FIG. 2, an entire structure of the secondary air control device will be described. The secondary air control device includes an air switching valve 1 for opening or closing an air passage, a one-way valve 2 for permitting airflow only in one direction and an electric motor 3 for driving the air switching valve 1. A driving force of the electric motor 3 is transmitted through a valve driving mechanism (shown in FIG. 1) to a poppet valve 4 of the air switching valve 1. All of these components of the secondary air control device are contained in a housing composed of a valve case 11, an outlet case 13 and case cover 12 (shown in FIG. 3).

An air pump for supplying the secondary air to an inlet port 17 of the air switching valve 1 and the electric motor 3 are controlled by an ECU (Electronic Control Unit) according to driving conditions of the engine. The ECU is a known microcomputer including a CPU (Central Processing Unit) and memories (ROM, RAM) for storing programs and data. A temperature of the three-way catalizer is detected and inputted to the ECU. When the catalizer temperature is lower than a predetermined level, at a starting up of the engine, the air pump and the electric motor 3 are driven to supply the secondary air to the three-way catalizer.

The valve case 11 is made of a metallic material such as die-cast aluminum having a high thermal conductivity. In the valve case 11, a valve seat 14 having a valve port 15 which is closed or opened by the poppet valve 4 and an inlet pipe 16 for introducing air to the valve port 15 are integrally formed. The valve seat 14 may be formed separately from the valve case 11 and installed to the valve case 11. The inlet pipe 16 is connected to the air pump through the secondary air passage (not shown) and includes an inlet passage 18 extending substantially straight from the inlet port 17 to the valve port 15 with an inclination. The inlet passage 18 is connected to the valve port 15 through another inlet passage 19. The one-way valve 2 having an air passage 21 is disposed downstream of the valve port 15, and the valve port 15 is connected to the air passage 21 through a passage 20.

The case cover 12 (shown in FIG. 3) is made of a resin material and has a connector shell 22. The secondary air control device is electrically connected to the ECU through a wire harness that has female terminals to be coupled to male terminals 23 formed in the connector shell 22. The outlet case 13 is made of a metallic material such as die-cast aluminum and has an outlet port 28 for delivering the secondary air therethrough. The valve case 11 and the outlet case 13 are connected to each other by abutting respective connecting flanges 24, 25. A circular seal rubber 27 for sealing the connecting portion is disposed between both flanges 24, 25. A metal plate 35 of the one-way valve 2 is disposed in a mounting portion 26 formed in the outlet case 13 and sandwiched between the valve case 11 and the outlet case 13. The outlet port 28 and the passage 21 of the one-way valve 2 are connected through an outlet passage 29.

The outlet case 13 forming the housing together with the valve case 11 and case cover 12 includes a mounting stay 30 having bolt holes 31. The outlet case 13 is fixedly connected to a secondary air passage tube or an exhaust gas passage communicating with the outlet port 28 with mounting bolts (not shown) inserted into the bolt holes 31.

The air switching valve 1 includes a poppet valve 4 composed of a valve head 5 and a valve shaft 6, both being integrally formed by molding a resin material. The valve head 5 and the valve shaft 6 may be separately made and connected to each other. The poppet valve 4 is reciprocally driven (in the vertical direction in FIG. 2) by the driving mechanism including the electric motor 3, and thereby the valve port 15 is opened or closed by the valve head 5. The valve head 5 includes a seal rubber 32 fixedly connected to an outer peripheral portion of the valve head 5. The seal rubber 32 contacts the valve seat 14 to thereby seal the valve port 14 when the valve port 15 is closed. The valve head 5 is separated from the valve seat 14 and positioned in the passage 20 when the valve port 15 is opened. A lower part of the valve shaft 6 is formed in a cylindrical shape, and an upper part in a solid rod having a rack 49 thereon, as shown in FIG. 2.

The one-way valve 2 is positioned downstream of the valve port 15. The one-way valve 2 is composed of a metal plate 35 having an air passage 21, a reed valve 33 for opening or closing the air passage 21 and a stopper 34 for limiting movement of the reed valve 33. The metal plate 35 is fixedly held between the valve case 11 and the outlet case 13, and the reed valve 33 and the stopper 34 are fixed to the metal plate 35 at their one ends with a rivet or the like. The reed valve 33 is made of a thin metallic plate such as a spring plate and formed in a double- or triple-tongue shape so that it resiliently moves to open or close the air passage 21. The stopper 34 is made of a metallic plate and formed in a double- or triple-tongue shape. The maximum movement of the reed valve 33 is limited by the stopper 34 when the reed valve 33 opens the air passage 21. The reed valve 33 opens the air passage 21 by a pressure of the secondary air to be supplied to the three-way catalyzer in the exhaust pipe. The reed valve 33 closes the air passage 21 to prevent the exhaust gas from entering into the air control device. The air passage 21 is formed in a mesh-like shape having plural openings.

Now, referring FIGS. 1-4, how the poppet valve 4 is driven will be described. As better seen in FIG. 1, the valve shaft 6 of the poppet valve 4 is reciprocally driven in its axial direction by a valve-driving mechanism composed of the electric motor 3 and a speed reduction mechanism including plural gears. The poppet valve 4 is biased in a direction to close the valve port 15 by a torsion spring 10 wound around a final gear 9. The poppet valve 4 opens the valve port 15 when it is driven by the motor 3.

The electric motor 3 is a known brushless DC motor including a rotor connected to a motor shaft 36 and a stator disposed outside of the rotor. The rotor has permanent magnets, and the stator has an armature winding disposed in a cylindrical yoke 37. Electric power is supplied to the motor 3 from terminal 38 extending from a motor housing and connected to the terminals 23 (refer to FIG. 3). The motor 3 is driven under control of the ECU. The motor 3 is contained and fixedly held in a motor hole 67 of the valve case 11 as shown in FIG. 3. A pinion gear 7 constituting part of the speed reduction mechanism is connected to the motor shaft 36. In place of the brushless DC motor 3, other motors such as a DC motor with brushes or a three-phase induction motor may be used.

As shown in FIG. 1, the speed reduction mechanism is composed of the pinion gear 7 connected to the motor shaft 36, an intermediate gear 8 and a final gear 9. The pinion gear 7 engages with a large gear 40 of the intermediate gear 8. The diameter of the large gear 40 is much larger than the diameter of the pinion gear 7. The intermediate gear 8 also has a small gear 42, and both of the large gear 40 and the small gear 42 are commonly held by a supporting shaft 41 which is rotatably supported in the housing. The final gear 9 includes an axis 44, a pie-shaped gear portion 43 engaging with the small gear 42 of the intermediate gear 8 and a pinion 46 (having teeth 47) engaging with the rack 49 of the valve shaft 6. The final gear 9 further includes a flange 45 around which the torsion spring 10 biasing the valve shaft in the direction of closing the valve port 15 is wound. A first end 51 of the torsion spring 10 is connected to first hook formed on the flange 45, and a second end 53 of the torsion spring 10 is fixed to a second hook 54 held in the housing. Though the pinion 46 engaging with the rack 49 is formed all around the axis 44 in this embodiment, it may be formed only at a portion corresponding to the rack 49.

As shown in FIGS. 1 and 3, the torsion spring 10 (a coil spring) is disposed in a cylindrical space between the pinion 46 engaging with the rack 49 and the pie-shaped gear portion 43. When the valve shaft 6 is driven in the direction to open the valve port 15, a resilient force is accumulated in the torsion spring 10. As shown in FIGS. 2-4, a cylindrical spring guide 62 having a spring space 61 therein, a cylindrical valve guide 64 having a hole 63 slidably containing the valve shaft 6 therein, a gear box 66 forming a gear chamber 65 therein, and a motor case 39 forming a motor hole 67 therein are integrally formed in the valve case 11. An inner bore of the spring guide 62 functions as a bore for guiding an outer diameter of the torsion spring 10. As shown in FIG. 2, a ring-shaped seal rubber 69 is disposed in the valve guide 64 to prevent leakage of the secondary air from the inlet passage 19. The gear box 66 contains the speed reduction mechanism including the pinion gear 7, the intermediate gear 8 and the final gear 9.

Operation of the secondary air control system described above will be explained. The three-way catalyzer for converting harmful components such as CO, HC and NOx in the exhaust gas to harmless components is installed in the exhaust pipe. In particular, HC (hydrocarbon) is oxidized in the three-way catalyzer and converted into water and carbon-dioxides. However, the three-way catalyzer does not function effectively if air-fuel mixture supplied to the engine is not stoichiometric (15:1). Further, the three-way catalyzer does not work properly when a temperature of the exhaust gas is low.

In order to activate the three-way catalyzer, secondary air generated by the air pump is supplied to the three-way catalyzer through the secondary air control device. The exhaust gas temperature is raised by oxidizing unburned components with the secondary air, and thereby the three-way catalizer is activated. Therefore, when the exhaust gas temperature is lower than a predetermined level (under conditions such as starting up of the engine), the secondary air is supplied to the three-way catalyzer. The temperature may be detected by an exhaust gas temperature sensor or a sensor for detecting the temperature of the three-way catalyzer. The air pump and the secondary air control device are operated under the control of the ECU to which the detected temperature is fed.

When the electric motor 3 is driven, its rotational torque is transmitted to the poppet valve 4 through the speed reduction mechanism. More particularly, the motor torque is first transmitted from the pinion gear 7 connected to the motor shaft 36 to the large gear 40 of the intermediate gear 8. Then, the rotational torque is further transmitted from the small gear 42 to the gear portion 43 of the final gear 9. Then, the rotating torque of the pinion 46 of the final gear 9 is converted into a linear movement of the rack 49 engaging with the pinion 46. Thus, the valve shaft 6 is driven in the direction to open the valve port 15. When power supply to the motor 3 is terminated, the valve shaft 6 returns to its original position by the biasing force of the torsion spring 10 to thereby close the valve port 15.

Since the rotational torque of the motor 3 is transmitted, through the speed reduction mechanism including the pinion gear 7, the large gear 40, the small gear 42 and the gear portion 43, to the pinion 46 of the final gear 9, the rotational speed is reduced by an amount of the gear ratio in the speed reduction mechanism. An amount of opening degree of the valve port 15 is also controlled by the ECU.

The secondary air is supplied from the air pump to the three-way catalyzer through the secondary air control device. More particularly, the secondary air is supplied from the air pump through: the inlet port 17 of the inlet pipe 16, the inlet passages 18, 19, the valve port 15, the passage 20, the air passage 21 in the one-way valve 2, the outlet passage 29 in the outlet case 13, and the outlet port 28. In this manner, the three-way catalyzer temperature is raised by oxidation of unburned components by the secondary air, and the three-way catalyzer is activated. Thus, the harmful components in the exhaust gas are effectively converted into harmless components.

Advantages attained in the embodiment described above will be summarized. Since the torsion spring 10 is wound around the flange 45 of the final gear 9, the length of the valve shaft 6 is shortened (conventionally, a coil spring is disposed around the valve shaft). Therefore, the secondary air control device can be made compact, saving its mounting space in an engine compartment. The housing containing the secondary air control device connected to the secondary air passage pipe or the exhaust pipe in a cantilever fashion has a higher strength against vibration because a distance from the mounting stay 30 of the housing to the other end of the device is made shorter. In other words, a cantilever length of the housing is shortened.

Since the pinion 46 of the final gear 9 is firmly engaged with the rack 49 of the valve shaft 6 by the biasing force of the torsion spring 10 even when the motor 3 is not driven, abrasion wear of the pinion 46 and the rack 49 due to vibration of the engine can be minimized. Since the cylindrical space between the pinion 46 and the gear portion 43 of the final gear 9 is utilized for disposing the torsion spring 10, the size of the secondary air control device is further reduced. Since the pinion 46 of the final gear 9 is firmly engaged with the rack 49 by the biasing force of the torsion spring 10, engaging wear of the pinion 46 and the rack 49 can be suppressed. Since the torsion spring 10 is positioned closer to the motor 3 in this embodiment than in the conventional device, a detent torque of the motor 3 for keeping an open position of the poppet valve 4 can be effectively utilized.

The present invention is not limited to the embodiment described above, but it may be variously modified. For example, the present invention may be applied to devices other than the secondary air control device, such as intake air control valves (swirl control valves, tumble control valves) or valves for controlling amount of intake air (throttle valves, idling speed control valves). The present invention may be applied to an exhaust gas recirculation control valve (EGR control valve). In this case, the one-way valve may be eliminated. Further, the present invention may be applied to valves for opening or closing a fluid passage, valves for intercepting a fluid passage, valves for controlling an amount of fluid, or valves for controlling a pressure of fluid. The fluid is not limited to air, but it may be other gases such as evaporated fuel, water, liquid fuel, oil or other liquids. Further, the fluid may be a mixture of gaseous and liquid state fluids such as refrigerant in an air-conditioner.

Though an electric motor is used for driving the poppet valve 4, other drivers such as an electromagnetic actuator having a solenoid coil may be used. In place of the poppet valve 4, other valves, such as a rotary valve, a butterfly valve, a shutter valve or a ball valve, may be used. A valve shaft and a valve body may be separately formed and they may be connected thereafter. The one-way valve may be eliminated in certain applications. The reed valve 33 and the stopper 34 may be riveted together at their one end, fastened by a screw, or connected together by staking or the like. The one-way valve 2 may be positioned at the outlet port 28. The valve case 11 and the outlet case 13 may be combined into a single body. An outlet pipe may be connected to the outlet port 28. The torsion spring 10 may be replaced with a torsion bar or a leaf spring, a double-coil spring, or a coil spring having an uneven pitch.

While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims. 

1. An air control device comprising: a housing having a valve port formed therein; a valve disposed in the housing for opening or closing the valve port, the valve having a valve shaft and a valve head; a valve driving mechanism including an electric motor, a speed reduction mechanism having a plurality of gears including a final gear engaging with a rack formed on the valve shaft so that a rotational movement of the final gear is converted to a linear movement of the valve shaft for opening or closing the valve port; and biasing means for biasing the valve in a direction to close the valve port, wherein: the biasing means is disposed around an axis of the final gear.
 2. The air control device as in claim 1, wherein: the axis of the final gear is disposed perpendicularly to the valve shaft.
 3. The air control device as in claim 2, wherein: the biasing means is a torsion spring wound around the axis of the final gear.
 4. The air control device as in claim 3, wherein: a torsional resilient force is accumulated in the torsion spring when the axis of the final gear is driven in a direction to open the valve port.
 5. The air control valve as in claim 2, wherein: the rack is formed on the valve shaft at its end portion opposite to an end where the valve head is connected; and the rack engages with a pinion connected to the axis of the final gear.
 6. The air control valve as in claim 1, wherein: the valve driving mechanism is contained in the housing together with the valve; and the housing is fixed to an air passage communicating with the valve port in a cantilever fashion.
 7. The air control valve as in claim 1, wherein: the air control device controls airflow of secondary air supplied from an air pump to a calalyser in an exhaust pipe of an automotive vehicle.
 8. The air control valve as in claim 7, further comprising a one-way valve for preventing exhaust gas from flowing into the valve port while permitting the secondary air to flow out through the valve port.
 9. An air control device comprising: a housing having a valve port formed therein; a valve disposed in the housing for opening or closing the valve port, the valve having a valve shaft and a valve head; a valve driving mechanism including an electric motor, a speed reduction mechanism having a plurality of gears including a final gear engaging with a rack formed on the valve shaft so that a rotational movement of the final gear is converted to a linear movement of the valve shaft for opening or closing the valve port; and biasing means for biasing the valve in a direction to open the valve port, wherein: the biasing means is disposed around an axis of the final gear. 